There is a type of compressors that is called a turbo compressor. Turbo compressors are used in a variety of applications such as air conditioners.
As disclosed in Patent Document 1, turbo compressors have a problem called surging. Surging is a phenomenon in which, for example, when a load of a compressor in operation is suddenly changed from a high load to no load, the flow rate of the fluid (refrigerant) in the entire flow path including the compressor becomes unstable, and pipes or other elements which constitute the compressor and the flow path resonate, so that the pressure and the flow rate periodically fluctuate. Surging causes not only the instable operating state of the compressor, but also damage to the compressor.